Several third generation wireless communication systems are being developed. One such third generation wireless communication system is known as CDMA 2000. In CDMA 2000, a variety of techniques are being incorporated for improving call quality. Open loop transmit diversity is one Such technique in which user signals are transmitted using two antennas. In a first phase of CDMA 2000, open loop transmit diversity is currently being implemented in a form of orthogonal transmit diversity (OTD). In OTD, separate antennas are used to transmit even data bits and odd data bits to achieve transmit diversity and improved call quality.
In a second phase of CDMA 2000, open loop transmit diversity may be implemented in a for in of space time spreading (STS) using Walsh functions or codes. STS enhances call quality by providing variable gain over OTD depending on the coding rate being used. Specifically, in STS, odd data bits and even data bits are jointly, not separately, transmitted over two antennas. However, the manner in which tile odd and even data bits are modulated/processed before being transmitted over one antenna will be different from the manner in which the odd and even data bits are modulated/processed being transmitted over the other antenna.
There has been some concern that including both open loop transmit diversity schemes as options in CDMA 2000 would be very complex in terms of implementing them into a common transmitter architecture. Accordingly, there exists a need for a simple to implement common receiver architecture that has incorporated orthogonal transmit diversity and space time spreading schemes.